1. Field of the Invention
This invention relates in general to antenna systems, and in particular to a dual coverage grid method for increased signal coverage.
2. Description of Related Art
Communications satellites have become commonplace for use in many types of communications services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, satellites must provide signals to various geographic locations on the Earth""s surface. As such, typical satellites use customized antenna designs to provide signal coverage for a particular country or geographic area.
In order to provide signal coverage over a large area, several approaches are used. A single beam with a wide beamwidth is sometimes used, but is limited in terms of power delivery over such a large geographic area. Typically, to cover a large geographic area, contiguous spot beams are used.
Contiguous spot beams are generated by multiple antennas to cover a large geographic area with a small variation in measured signal strength at the ground. The contiguous beams typically generate a grid that provides a certain Effective Incident Radiated Power (EIRP) throughout the coverage area for the spacecraft. However the EIRP that can be delivered by a given spacecraft and/or antenna system is limited by amplifier power, bandwidth, and antenna size.
Other advances for satellite communications have come in the personal communications system (PCS) system, or world-wide cellular telephony. Typical cellular telephony uses cell division to increase signal throughput in certain high-traffic areas. These smaller additional cells are created by installing additional antenna sites at each cell. Similarly, satellites can create smaller grid cells by using additional beams, transmitters, and antennas.
However, since each satellite is limited in the number of antennas, transmitters, and beams that it can support, adding more hardware to the system is typically cost prohibitive.
It can be seen, then, that there is a need in the art for antenna systems that can deliver contiguous spot beams over large geographic areas that can carry additional signals. It can also be seen that there is a need in the art for antenna systems that can deliver signals for mobile applications without signal interruption. It can also be seen that there is a need in the art for antenna systems that provide ease of mechanical design and construction to reduce spacecraft costs.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for producing contiguous spot beam communications coverage on the Earth""s surface. The apparatus comprises two contiguous beam patterns. The first contiguous beam pattern comprises a first set of cells and has a first set of frequencies. The second contiguous beam pattern comprises a second set of cells and has a second set of frequencies. The second contiguous beam pattern is spatially offset from the first contiguous beam pattern such that an edge of the first set of cells is offset from an edge of the second set of cells.
The method comprises the steps of producing a first contiguous spot beam pattern on the Earth""s surface, producing a second contiguous spot beam pattern on the Earth""s surface, and overlapping the first contiguous spot beam pattern and the second contiguous spot beam pattern such that an edge of the first contiguous spot beam pattern is offset from an edge of the second contiguous spot beam pattern.
The present invention provides antenna systems that can deliver contiguous spot beams over large geographic areas that can carry additional signals. The present invention also provides antenna systems that can deliver signals for mobile applications without signal interruption. The present invention also provides antenna systems that provide ease of mechanical design and construction to reduce spacecraft costs.